What about the Core interpreter in fptools/ghc/utils/ext-core ?

There's a Happy parser source file there, Parser.y, as well as all sorts of other Core-related goodies.

FYI, one can use the parser and printer in fptools/ghc/utils/ext-core as is, but the typechecker and interpreter need updating in order to work with Core emitted by the latest version of GHC (the changes should be pretty minor, but I haven't tried to make them). -- Kirsten Chevalier * krc@uclink.berkeley.edu * Often in error, never in doubt